NOAA updates Atlantic hurricane outlook

"Arthur" was the earliest N.C. hurricane in centuries, but the overall season is expected to be below average.

NWS radar data of Hurricane Arthur / July 4, 2014 / 3 a.m.

The odds of a quieter-than-average 2014 Atlantic Basin hurricane season appear to be improving, according to the latest Climate Prediction Center (CPC) outlook.

The updated forecast released August 7 calls for only a five percent probability of an above-normal number of tropical storms/hurricanes in the Atlantic, Caribbean and Gulf of Mexico while there is now a 70 percent chance that the atmosphere will churn out fewer tropical cyclones than in a typical season. The CPC forecasters say there’s a 25 percent chance the season will have an average number of named storms.

A (named) tropical storm is declared when a closed warm-core surface low pressure area generates sustained winds of 39 to 73 mph, it becomes a hurricane when sustained winds reach 74 mph or higher.

The 30-year average is for 12 named storms, six of which are hurricanes, and three “major” hurricanes (winds of 111 mph or greater).

This year’s outlook calls for 7 to 12 storms total with 3 to 6 hurricanes and 0 to 2 major hurricanes. The August update toned down an already subdued outlook issued in May. The forecast at that time called for a 50 percent chance of a “quiet” season with 1 or 2 major hurricanes and 8 to 13 storms total.

Forecasters cite these factors in their adjusted forecast:

“Overall atmospheric conditions are not favorable for storm development. This includes strong vertical wind shear, a weaker West African monsoon, and the combination of increased atmospheric stability and sinking motion. These conditions mean fewer tropical systems are spawned off the African coast, and those that do form are less likely to become hurricanes. These conditions are stronger than originally predicted in May and are expected to last Mid-August through October, the peak months of the hurricane season.

Overall oceanic conditions are not favorable for storm development. This includes below-average temperatures across the Tropical Atlantic, which are exceptionally cool relative to the remainder of the global Tropics. This cooling is even stronger than models predicted in May and is expected to persist through the hurricane season.

El Niño is still likely to develop and to suppress storm development by increasing vertical wind shear, stability and sinking motion in the atmosphere.”

Hurricane Arthur was the first named system of the 2014 Atlantic season; it formed off of Florida and moved northward, making landfall in eastern North Carolina late on July 3. It was the earliest hurricane on record for that state. Arthur was a Category Two with winds of 100 mph, but the overall damage from the storm was quite low. “Bertha” formed on July 31 but remained at sea. It tracked northeastward and dissipated over colder north Atlantic waters on August 6.